You're not wrong. It's why I rounded everything into, "Coin". Essentially the rent or upkeep is a known as Inanis house she buys you is listed in the Market, so you know the amount and the years involved can be understood as sets of months. So Year 1 Month 5, a year of upkeep later is Year 2 Month 5 - still whole.
However, as you put it, resolving it to make it simpler, or more elegant, is a goal. So what to do? My thought was two fold, one being: Buy the house and upkeep up front, more or less depending on how many years of upkeep you want to buy. Or, two, just put a hard upkeep cost at the end of each year, how much of that year you got to actually live in the shelter be damned.
2D presentation. I wouldn't even know where to begin with 3D or 3D animation. I won't pretend to be wholly practical, but I do know my limits to some degree. Also since I've been learning to draw while doing the "Effort" line of CYOAs, I figured that was the best place to start, also I just wanted to see if I could animate a sprite. Mess that it ended up being, it was still a fun experience and I did learn a few things from the effort. Perhaps not elegant, more blunt force . . . it'll require a rewrite regardless.
It's a 2D effort, and not a serious one. When my hands get antsy I go for learning new things as a break from the norm. 3D just seemed completely out of my league, so I went for something that could benefit from the drawing skill I've been working on as the "Effort" images progressed, because of them really.